THIS INVENTION concerns a technique and an instrument for on-site detection of trace volatiles, in gaseous, vapour or liquid phase, particularly, though not exclusively, those generated by timber decay fungii.
Fungal attack of construction timbers can progress, sometimes unnoticed, to a state where the timber is weakened sufficiently to compromise building safety. The fungus which results in dry-rot is Serpula lacrymans which grows readily in areas such as cellars, behind panelling and plaster, and in sub-floor spaces thus making it difficult to detect the presence of such fungus at an early stage.
It is therefore an object of the present invention to provide a method of and instrument for the detection of such fungus to provide an aid to early diagnosis thus minimising costs associated with fungal damage and disruption caused by remedial investigations.
Odours emitted from wood-rotting fungus comprise defined volatile organic compounds which are indicative of fungal infection on timber. A distinctive mushroom-like odour accompanies Serpula lacrymans growth. The mushroom-like odour is derived from a complex mixture of trace volatiles, some of which may be used as unique markers for detection of Serpula lacrymans. 
The method and instrument described herein is intended particularly, though not exclusively, for the detection of dry-rot fungus but may be adapted for use also in the detection of other fungal species and of pest infestations such as are caused by rats, cockroaches and termites, since such pests also give off odours or trace volatile chemicals. Indeed, there are many potential applications for the present invention, where trace volatiles are present in gaseous, vapour or liquid phase, and can be detected using the present method and instrument, simply modified to detect the appropriate chemical odour.
As a matter of practicality it is also an object of the present invention to provide an instrument which may be used by semi-skilled personnel or property surveyors in the field, the instrument being portable and thus capable of being deployed, without damage, in the most cramped and inaccessible of sites.
The instrument will be used in conjunction with computer software including mathematical algorithms which when applied to signals generated by the instrument will produce a response which effectively provides a fingerprint for the location and identification of the presence of trace volatiles, even in the presence of background odours.
The instrument may include known technology employing an array of commercially available sensors coupled to electronic apparatus for data acquisition and analysis.
The discriminatory capability of sensor arrays relies upon the utilisation of cross-sensitivities between individual sensors. In such an array the individual sensors possess slightly different responses to odour volatiles, and these differences provide sufficient information to discriminate between different odour volatiles. Such an array of sensors combined with electronic analytical computer equipment and suitable mathematical methods may be referred to as an “electronic nose”. Typically, such a device consists of three elements, namely, the sensor array which is exposed to the trace volatiles, means for conversion of the sensor outputs to a readable format and means to perform software analysis of the data to produce a fingerprint representative of a particular set of trace volatiles. The output from the sensor array may be interpreted via a variety of methods such as pattern recognition algorithms, principal component analysis, discriminant function analysis, cluster analysis and artificial neural networks to discriminate between samples.
A variety of sensor types may be adopted, for example, quartz crystal sensors in which the crystal oscillates in an electrical field and its change of frequency, brought about by the presence of trace volatiles, can be measured. Other kinds of sensor include surface acoustic wave sensors including a piezo-electric substrate onto which is deposited a thin film coating of a selective material. An applied radio frequency voltage produces a surface acoustic wave on such material, and adsorption of odour volatiles onto the coating increases its mass and disturbs the wave leading to a shift in frequency, which can be measured. Another type of sensor may be taken from several available types of resistive sensors and in this particular example the preferred type is a metal oxide semiconductor sensor whose electrical resistance changes in the presence of odour volatiles. Such sensors also have the advantage that they perform as heaters whereby the ambient temperature within a chamber containing an array of such sensors may be elevated to cause trace volatiles to be desorbed from a carrier coating.
In a typical environmental application, the consistent collection and delivery of odour volatiles into an “electronic nose” may be problematic. A number of factors contribute to this, namely inherent environmental variables such as temperature and humidity, and physical parameters such as site accessibility and air-borne particulates such as dust. Also, site-specific background interference odours and low concentration target volatiles may contribute to the complexity of the detection technique.